As a shift drum drive mechanism of a transmission, there has been well known a so-called manual transmission which performs a gear change actuation by operating a foot-operated pedal and the like to drive a shift spindle and to turn a shift drum. Moreover, there has been known an electric transmission which performs a gear change actuation by driving a shift drum of the transmission by use of an electric motor. For example, one of such electric transmissions adopts a driving method for driving a shift spindle by use of an electric motor instead of the foot-operated pedal operation described above while adhering fundamentally to a driving method for driving a shift spindle by use of the foot-operated pedal operation. For example, see Japanese Patent Laid-Open No. Hei 11 (1999)-82734 (Pages 4 and 5, FIG. 5)
Furthermore, as another method of the electric transmission described above, there has been known a method for driving a shift drum by use of an intermittent feed mechanism that is a Geneva stop mechanism. For example, see Japanese Patent Laid-Open No. Hei 5 (1993)-39865 (Pages 3 and 4, FIG. 5). This electric transmission has a structure in which structural parts related to driving of the drum, in other words, an electric motor that is a driving source for the drum, a gear driving mechanism for transmitting a driving force of the motor, the Geneva stop mechanism that is the intermittent feed mechanism, and the like are concentrated and disposed on one side of the shift drum.
Moreover, there has been also known a transmission which changes gears by selectively driving rotation of a shift drum by use of an electric motor or a manual operation of a knob and the like.
Incidentally, a kind of modification example, described above, of the conversion from the foot-operated shift drum driving method in a vehicle equipped with the known manual transmission to the driving by use of the electric motor can be perceived as the transmission described in Japanese Patent Laid-Open No. Hei 11 (1999)-82734 described above. This driving method is an improved method in which foot-operated drive of the shift spindle is changed to the driving by use of the electric motor. This improved driving method achieves the sharing of many parts while maintaining a basic structure of foot-operated shift drum drive.
In the method described above, it is hoped that a certain degree of margin of capacity and size is provided for the electric motor because an output of a driving source, that is, an output of the electric motor needs to correspond to a spring for fixing a position of the shift drum and a return spring of the shift spindle. Moreover, this method adheres to the structure of the manual transmission in that the shift spindle is extended parallel to the shift drum on the outside thereof. Thus, there is also a desire to simplify the structure for the addition of the motor.
Moreover, an improvement based on the shift drum driving method by use of the electric motor according to Japanese Patent Laid-Open No. Hei 5 (1993)-39865 described above has a characteristic that, in this driving method, the electric motor that is the driving source for the shift drum, the gear driving mechanism, the intermittent feed mechanism, and the like are concentrated and disposed on one side of the shift drum. Thus, this shift drum driving method is significantly different from the manual driving method described above in terms of the structure. Consequently, there will be many changes in the structure along with a change of the manual driving method into a motorized method.
In consideration of the foregoing problems, it is an object of the present invention to achieve the sharing of parts while maintaining the foot-operated shift drum driving method in the manual transmission described above, and to obtain an electrical shift drum driving method which is simplified by a minimum structural change.